Fluid handling structure, lithographic apparatus and device manufacturing method

ABSTRACT

A fluid handling structure for a lithographic apparatus is disclosed, the fluid handling structure successively has, at a boundary from a space configured to contain immersion fluid to a region external to the fluid handling structure: an elongate opening or a plurality of openings arranged in a first line that, in use, are directed towards a substrate and/or a substrate table configured to support the substrate; a gas knife device having an elongate aperture in a second line; and an elongate opening or a plurality of openings adjacent the gas knife device.

This application is a continuation of U.S. patent application Ser. No.15/838,634, filed Dec. 12, 2017, now allowed, which is a continuation ofU.S. patent application Ser. No. 15/016,041, filed on Feb. 4, 2016, nowU.S. Pat. No. 9,846,372, which is a continuation of U.S. patentapplication Ser. No. 13/090,311, filed on Apr. 20, 2011, now U.S. Pat.No. 9,256,136, which claims priority and benefit under 35 U.S.C. §119(e) to U.S. Provisional Patent Application Ser. No. 61/326,972,entitled “Fluid Handling Structure, Lithographic Apparatus and DeviceManufacturing Method”, filed on Apr. 22, 2010, and to U.S. ProvisionalPatent Application Ser. No. 61/362,961, entitled “Fluid HandlingStructure, Lithographic Apparatus and Device Manufacturing Method”,filed on Jul. 9, 2010. The contents of those applications areincorporated herein in their entirety by reference.

FIELD

The present invention relates to a fluid handling structure, alithographic apparatus and a method for manufacturing a device.

BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits (ICs). In that instance, a patterning device, whichis alternatively referred to as a mask or a reticle, may be used togenerate a circuit pattern to be formed on an individual layer of theIC. This pattern can be transferred onto a target portion (e.g.comprising part of, one, or several dies) on a substrate (e.g. a siliconwafer). Transfer of the pattern is typically via imaging onto a layer ofradiation-sensitive material (resist) provided on the substrate. Ingeneral, a single substrate will contain a network of adjacent targetportions that are successively patterned. Known lithographic apparatusinclude so-called steppers, in which each target portion is irradiatedby exposing an entire pattern onto the target portion at one time, andso-called scanners, in which each target portion is irradiated byscanning the pattern through a radiation beam in a given direction (the“scanning”-direction) while synchronously scanning the substrateparallel or anti-parallel to this direction. It is also possible totransfer the pattern from the patterning device to the substrate byimprinting the pattern onto the substrate.

It has been proposed to immerse the substrate in the lithographicprojection apparatus in a liquid having a relatively high refractiveindex, e.g. water, so as to fill a space between the final element ofthe projection system and the substrate. In an embodiment, the liquid isdistilled water, although another liquid can be used. An embodiment ofthe present invention will be described with reference to liquid.However, another fluid may be suitable, particularly a wetting fluid, anincompressible fluid and/or a fluid with higher refractive index thanair, desirably a higher refractive index than water. Fluids excludinggases are particularly desirable. The point of this is to enable imagingof smaller features since the exposure radiation will have a shorterwavelength in the liquid. (The effect of the liquid may also be regardedas increasing the effective numerical aperture (NA) of the system andalso increasing the depth of focus.) Other immersion liquids have beenproposed, including water with solid particles (e.g. quartz) suspendedtherein, or a liquid with a nano-particle suspension (e.g. particleswith a maximum dimension of up to 10 nm). The suspended particles may ormay not have a similar or the same refractive index as the liquid inwhich they are suspended. Other liquids which may be suitable include ahydrocarbon, such as an aromatic, a fluorohydrocarbon, and/or an aqueoussolution.

Submersing the substrate or substrate and substrate table in a bath ofliquid (see, for example, U.S. Pat. No. 4,509,852) is a form ofimmersion system arrangement. The arrangement requires that a large bodyof liquid should be accelerated during a scanning exposure. This mayrequire additional or more powerful motors and turbulence in the liquidmay lead to undesirable and unpredictable effects.

In an immersion apparatus, immersion liquid is handled by a fluidhandling system or apparatus, for example a fluid handling structure. Afluid handling system may supply immersion fluid and therefore be afluid supply system. A fluid handling system may confine fluid andthereby be a fluid confinement system. A fluid handling system mayprovide a barrier to fluid and thereby be a barrier member. A fluidhandling system may create or use a flow of fluid (such as gas), forexample to help in handling liquid. Immersion liquid may be used as theimmersion fluid. In that case, the fluid handling system may be a liquidhandling system.

One of the arrangements proposed is for a liquid supply system toprovide liquid on only a localized area of the substrate and in betweenthe final element of the projection system and the substrate using aliquid confinement system (the substrate generally has a larger surfacearea than the final element of the projection system).

One way which has been proposed to arrange for this is disclosed in PCTpatent application publication no. WO 99/49504. This type of arrangementmay be referred to as a localized immersion system arrangement.

Another arrangement is an all wet arrangement in which the immersionliquid is unconfined as disclosed in PCT patent application publicationWO 2005/064405. In such a system, the immersion liquid is unconfined.The whole top surface of the substrate is covered in liquid. This may beadvantageous because then the whole top surface of the substrate isexposed to the substantially same conditions. This may have an advantagefor temperature control and processing of the substrate. In WO2005/064405, a liquid supply system provides liquid to the gap betweenthe final element of the projection system and the substrate. Thatliquid is allowed to leak over the remainder of the substrate. A barrierat the edge of a substrate table prevents the liquid from escaping sothat it can be removed from the top surface of the substrate table in acontrolled way. Although such a system improves temperature control andprocessing of the substrate, evaporation of the immersion liquid maystill occur. One way of helping to alleviate that problem is describedin United States patent application publication no. US 2006/0119809. Amember is provided which covers the substrate W in all positions andwhich is arranged to have immersion liquid extending between it and thetop surface of the substrate and/or substrate table which holds thesubstrate.

In European patent application publication no. EP 1420300 and UnitedStates patent application publication no. US 2004-0136494, each herebyincorporated in their entirety by reference, the idea of a twin or dualstage immersion lithography apparatus is disclosed. Such an apparatus isprovided with two tables for supporting a substrate. Levelingmeasurements are carried out with a table at a first position, withoutimmersion liquid, and exposure is carried out with a table at a secondposition, where immersion liquid is present. Alternatively, theapparatus has only one table.

SUMMARY

It is desirable to be able to move the substrate as fast as possiblebelow the projection system. For this, the fluid handling system,especially for a localized area fluid handling system, should bedesigned to allow high scanning without significant liquid loss.

It is desirable, for example, to provide a fluid handling system whichmaintains liquid in a space between the final element of the projectionsystem and the substrate.

According to an aspect, there is provided a fluid handling structure fora lithographic apparatus, the fluid handling structure successivelyhaving, at a boundary from a space configured to contain immersion fluidto a region extemal to the fluid handling structure:

an elongate opening or a plurality of openings arranged in a first linethat, in use, is directed towards a substrate and/or a substrate tableconfigured to support the substrate;

a gas knife device having an elongate aperture in a second line; and

an elongate opening or a plurality of openings adjacent the gas knifedevice.

According to an aspect, there is provided a fluid handling structure fora lithographic apparatus, the fluid handling structure successivelyhaving, at a boundary of a space to which in use immersion liquid isconfined to a region external to the fluid handling structure:

an elongate opening or a plurality of openings to extract fluid andarranged in a first line that, in use, is directed towards a facingsurface of, for example, a substrate and/or a substrate table configuredto support the substrate;

an elongate aperture for a gas knife, in a second line;

an elongate opening or a plurality of openings to extract liquid andadjacent the elongate aperture for the gas knife device.

flow through the aperture 61 in the second line may be c apparatuscomprising a fluid handling structure as above.

According to an aspect, there is provided a device manufacturing method,comprising:

providing an immersion liquid to a space between a final element of aprojection system and a substrate and/or a substrate table configured tosupport the substrate;

retrieving immersion liquid from between the final element of theprojection system and the substrate and/or substrate table through anelongate opening or a plurality of openings arranged in a first line;

forcing immersion liquid towards the elongate opening or plurality ofopenings in the first line by supplying gas through an aperture in asecond line forming a gas knife;

extracting gas and remaining immersion liquid through an elongateopening or a plurality of openings adjacent the gas knife and on theopposite side of the gas knife to the elongate opening or plurality ofopenings in the first line.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 depicts a lithographic apparatus according to an embodiment ofthe invention;

FIGS. 2 and 3 depict a liquid supply system for use in a lithographicprojection apparatus;

FIG. 4 depicts a further liquid supply system for use in a lithographicprojection apparatus;

FIG. 5 depicts a further liquid supply system for use in a lithographicprojection apparatus;

FIG. 6 is a schematic illustration, in plan, of a meniscus pinningsystem according to an embodiment of the present invention;

FIG. 7 depicts, in cross-section in part along line VII-VII in FIG. 6and in a plane substantially perpendicular to a surface under a fluidhandling structure, a meniscus pinning system for use in an embodimentof the present invention;

FIG. 8 depicts, in cross-section in a plane substantially perpendicularto a surface under a fluid handling structure, a part of a fluidhandling structure according to an embodiment of the present invention;

FIG. 9 depicts, in cross-section in a plane substantially perpendicularto a surface under a fluid handling structure, a part of a fluidhandling structure according to a further embodiment of the presentinvention;

FIG. 10 depicts, in cross-section in a plane substantially perpendicularto a surface under a fluid handling structure, a part of a fluidhandling structure;

FIG. 11 depicts, in cross-section in a plane substantially perpendicularto a surface under a fluid handling structure, a part of a fluidhandling structure according to a further embodiment of the presentinvention;

FIG. 12 depicts, in cross-section in a plane substantially perpendicularto a surface under a fluid handling structure, a part of a fluidhandling structure according to a further embodiment of the presentinvention;

FIG. 13 depicts, in cross-section in a plane substantially perpendicularto a surface under a fluid handling structure, a part of a fluidhandling structure according to a further embodiment of the presentinvention; and

FIG. 14 depicts, in cross-section in a plane substantially perpendicularto a surface under a fluid handling structure, a part of a fluidhandling structure according to a further embodiment of the presentinvention.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a lithographic apparatus according to oneembodiment of the invention. The apparatus comprises:

-   -   an illumination system (illuminator) IL configured to condition        a radiation beam B (e.g. UV radiation or DUV radiation);    -   a support structure (e.g. a mask table) MT constructed to        support a patterning device (e.g. a mask) MA and connected to a        first positioner PM configured to accurately position the        patterning device in accordance with certain parameters;    -   a substrate table (e.g. a wafer table) WT constructed to hold a        substrate (e.g. a resist-coated wafer) W and connected to a        second positioner PW configured to accurately position the        substrate in accordance with certain parameters; and    -   a projection system (e.g. a refractive projection lens system)        PS configured to project a pattern imparted to the radiation        beam B by patterning device MA onto a target portion C (e.g.        comprising one or more dies) of the substrate W.

The illumination system may include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostaticor other types of optical components, or any combination thereof, fordirecting, shaping, or controlling radiation.

The support structure MT holds the patterning device. It holds thepatterning device in a manner that depends on the orientation of thepatterning device, the design of the lithographic apparatus, and otherconditions, such as for example whether or not the patterning device isheld in a vacuum environment. The support structure can use mechanical,vacuum, electrostatic or other clamping techniques to hold thepatterning device. The support structure may be a frame or a table, forexample, which may be fixed or movable as required. The supportstructure may ensure that the patterning device is at a desiredposition, for example with respect to the projection system. Any use ofthe terms “reticle” or “mask” herein may be considered synonymous withthe more general term “patterning device.”

The term “patterning device” used herein should be broadly interpretedas referring to any device that can be used to impart a radiation beamwith a pattern in its cross-section such as to create a pattern in atarget portion of the substrate. It should be noted that the patternimparted to the radiation beam may not exactly correspond to the desiredpattern in the target portion of the substrate, for example if thepattern includes phase-shifting features or so called assist features.Generally, the pattern imparted to the radiation beam will correspond toa particular functional layer in a device being created in the targetportion, such as an integrated circuit.

The patterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions. The tilted mirrorsimpart a pattern in a radiation beam which is reflected by the mirrormatrix.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system, including refractive,reflective, catadioptric, magnetic, electromagnetic and electrostaticoptical systems, or any combination thereof, as appropriate for theexposure radiation being used, or for other factors such as the use ofan immersion liquid or the use of a vacuum. Any use of the term“projection lens” herein may be considered as synonymous with the moregeneral term “projection system”.

As here depicted, the apparatus is of a transmissive type (e.g.employing a transmissive mask). Alternatively, the apparatus may be of areflective type (e.g. employing a programmable mirror array of a type asreferred to above, or employing a reflective mask).

The lithographic apparatus may be of a type having two (dual stage) ormore substrate tables (and/or two or more patterning device tables). Insuch “multiple stage” machines the additional tables may be used inparallel, or preparatory steps may be carried out on one or more tableswhile one or more other tables are being used for exposure.

Referring to FIG. 1, the illuminator IL receives a radiation beam from aradiation source SO. The source and the lithographic apparatus may beseparate entities, for example when the source is an excimer laser. Insuch cases, the source is not considered to form part of thelithographic apparatus and the radiation beam is passed from the sourceSO to the illuminator IL with the aid of a beam delivery system BDcomprising, for example, suitable directing mirrors and/or a beamexpander. In other cases the source may be an integral part of thelithographic apparatus, for example when the source is a mercury lamp.The source SO and the illuminator IL, together with the beam deliverysystem BD if required, may be referred to as a radiation system.

The illuminator IL may comprise an adjuster AM for adjusting the angularintensity distribution of the radiation beam. Generally, at least theouter and/or inner radial extent (commonly referred to as σ-outer andσ-inner, respectively) of the intensity distribution in a pupil plane ofthe illuminator can be adjusted. In addition, the illuminator IL maycomprise various other components, such as an integrator IN and acondenser CO. The illuminator may be used to condition the radiationbeam, to have a desired uniformity and intensity distribution in itscross-section.

The radiation beam B is incident on the patterning device (e.g., mask)MA, which is held on the support structure (e.g., mask table) MT, and ispatterned by the patterning device. Having traversed the patterningdevice MA, the radiation beam B passes through the projection system PS,which focuses the beam onto a target portion C of the substrate W. Withthe aid of the second positioner PW and position sensor IF (e.g. aninterferometric device, linear encoder or capacitive sensor), thesubstrate table WT can be moved accurately, e.g. so as to positiondifferent target portions C in the path of the radiation beam B.Similarly, the first positioner PM and another position sensor (which isnot explicitly depicted in FIG. 1) can be used to accurately positionthe patterning device MA with respect to the path of the radiation beamB, e.g. after mechanical retrieval from a mask library, or during ascan. In general, movement of the support structure MT may be realizedwith the aid of a long-stroke module (coarse positioning) and ashort-stroke module (fine positioning), which form part of the firstpositioner PM. Similarly, movement of the substrate table WT may berealized using a long-stroke module and a short-stroke module, whichform part of the second positioner PW. In the case of a stepper (asopposed to a scanner) the support structure MT may be connected to ashort-stroke actuator only, or may be fixed. Patterning device MA andsubstrate W may be aligned using patterning device alignment marks M1,M2 and substrate alignment marks P1, P2. Although the substratealignment marks as illustrated occupy dedicated target portions, theymay be located in spaces between target portions (these are known asscribe-lane alignment marks). Similarly, in situations in which morethan one die is provided on the patterning device MA, the patterningdevice alignment marks may be located between the dies.

The depicted apparatus could be used in at least one of the followingmodes:

1. In step mode, the support structure MT and the substrate table WT arekept essentially stationary, while an entire pattern imparted to theradiation beam is projected onto a target portion C at one time (i.e. asingle static exposure). The substrate table WT is then shifted in the Xand/or Y direction so that a different target portion C can be exposed.In step mode, the maximum size of the exposure field limits the size ofthe target portion C imaged in a single static exposure.2. In scan mode, the support structure MT and the substrate table WT arescanned synchronously while a pattern imparted to the radiation beam isprojected onto a target portion C (i.e. a single dynamic exposure). Thevelocity and direction of the substrate table WT relative to the supportstructure MT may be determined by the (de-)magnification and imagereversal characteristics of the projection system PS. In scan mode, themaximum size of the exposure field limits the width (in the non-scanningdirection) of the target portion in a single dynamic exposure, whereasthe length of the scanning motion determines the height (in the scanningdirection) of the target portion.3. In another mode, the support structure MT is kept essentiallystationary holding a programmable patterning device, and the substratetable WT is moved or scanned while a pattern imparted to the radiationbeam is projected onto a target portion C. In this mode, generally apulsed radiation source is employed and the programmable patterningdevice is updated as required after each movement of the substrate tableWT or in between successive radiation pulses during a scan. This mode ofoperation can be readily applied to maskless lithography that utilizesprogrammable patterning device, such as a programmable mirror array of atype as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

Arrangements for providing liquid between a final element of theprojection system PS and the substrate can be classed into three generalcategories. These are the bath type arrangement, the so-called localizedimmersion system and the all-wet immersion system. In the bath typearrangement substantially the whole of the substrate W and optionallypart of the substrate table WT is submersed in a bath of liquid.

The localized immersion system uses a liquid supply system in whichliquid is only provided to a localized area of the substrate. The spacefilled by liquid is smaller in plan than the top surface of thesubstrate. The volume or space filled with liquid remains substantiallystationary relative to the projection system PS while the substrate Wmoves underneath that area. FIGS. 2-5 show different supply deviceswhich can be used in such a system.

In the all wet arrangement the liquid is unconfined. The whole topsurface of the substrate and all or part of the substrate table iscovered in immersion liquid. The depth of the liquid covering at leastthe substrate is small. The liquid may be a film, such as a thin film,of liquid on the substrate. Immersion liquid may be supplied to or inthe region of a projection system and a facing surface facing theprojection system (such a facing surface may be the surface of asubstrate and/or a substrate table). Any of the liquid supply devices ofFIGS. 2-5 (which are described below) may be used in such a system.However, sealing features might not be present, might not be activated,might not be as efficient as normal or might otherwise be ineffective toseal liquid to only the localized area.

Four different types of localized liquid supply systems are illustratedin FIGS. 2-5. As illustrated in FIGS. 2 and 3, liquid is supplied by atleast one inlet onto the substrate as indicated by an arrow, preferablyalong the direction of movement of the substrate relative to the finalelement. Liquid is removed by at least one outlet after having passedunder the projection system as indicated by an arrow. As the substrateis scanned beneath the element in a −X direction, liquid is supplied atthe +X side of the element and taken up at the −X side. FIG. 2 shows thearrangement schematically in which liquid flow is indicated by arrows;the liquid is supplied via inlet and is taken up on the other side ofthe element by outlet which is connected to a low pressure source. Inthe illustration of FIG. 2 the liquid is supplied along the direction ofmovement of the substrate relative to the final element, although thisdoes not need to be the case. Various orientations and numbers of in-and out-lets positioned around the final element are possible; oneexample is illustrated in FIG. 3 in which four sets of an inlet with anoutlet on either side are provided in a regular pattern around the finalelement, as indicated by arrows.

A further immersion lithography solution with a localized liquid supplysystem is shown in FIG. 4. Liquid is supplied by two groove inlets oneither side of the projection system PS and is removed by a plurality ofdiscrete outlets arranged radially outwardly of the inlets. The inletscan be arranged in a plate with a hole in its centre and through whichthe projection beam is projected. Liquid is supplied by one groove inleton one side of the projection system PS and removed by a plurality ofdiscrete outlets on the other side of the projection system PS, causinga flow of a thin film of liquid between the projection system PS and thesubstrate W. The choice of which combination of inlet and outlets to usecan depend on the direction of movement of the substrate W (the othercombination of inlet and outlets being inactive). Note that thedirection of flow of fluid and of the substrate W is shown by arrows inFIG. 4.

Another arrangement which has been proposed is to provide the liquidsupply system with liquid confinement structure which extends along atleast a part of a boundary of the space between the final element of theprojection system and the substrate table. Such an arrangement isillustrated in FIG. 5. Arrows indicate the direction of flow.

FIG. 5 schematically depicts a localized liquid supply system or fluidhandling structure with a liquid confinement structure 12, which extendsalong at least a part of a boundary of the space 11 between the finalelement of the projection system PS and a facing surface (e.g. thesubstrate table WT or substrate W). (Please note that reference in thefollowing text to surface of the substrate W also refers in addition, orin the alternative, to a surface of the substrate table WT, unlessexpressly stated otherwise. Reference to movement of the substraterelative to another object, for example a projection system, includesreference to movement of the substrate table relative to the sameobject, unless expressly stated otherwise.) The liquid confinementstructure 12 is substantially stationary relative to the projectionsystem PS in the XY plane though there may be some relative movement inthe Z direction (in the direction of the optical axis). In anembodiment, a seal is formed between the liquid confinement structure 12and the surface of the substrate W. The seal may be a contactless sealsuch as a gas seal (such a system with a gas seal is disclosed in UnitedStates patent application publication no. US 2004-0207824) or fluidseal.

The liquid confinement structure 12 at least partly contains liquid inthe space 11 between a final element of the projection system PS and thesubstrate W. A contactless seal, such as a gas seal 16, to the substrateW may be formed around the image field of the projection system PS sothat liquid is confined within the space 11 between the substrate Wsurface and the final element of the projection system PS. The space 11is at least partly formed by the liquid confinement structure 12positioned below and surrounding the final element of the projectionsystem PS. Liquid is brought into the space 11 below the projectionsystem PS and within the liquid confinement structure 12 by liquid inlet13. The liquid may be removed by liquid outlet 13. The liquidconfinement structure 12 may extend a little above the final element ofthe projection system PS. The liquid level rises above the final elementso that a buffer of liquid is provided. In an embodiment, the liquidconfinement structure 12 has an inner periphery that at the upper endclosely conforms to the shape of the projection system PS or the finalelement thereof and may, e.g., be round or any other suitable shape. Atthe bottom, the inner periphery closely conforms to the shape of theimage field, e.g., rectangular, though this need not be the case.

The liquid may be contained in the space 11 by a gas seal 16 which,during use, is formed between the bottom of the liquid confinementstructure 12 and the surface of the substrate W. The gas seal 16 isformed by gas, e.g. air or synthetic air but, in an embodiment, N₂ oranother inert gas. The gas in the gas seal 16 is provided under pressurevia inlet 15 to the gap between liquid confinement structure 12 andsubstrate W. The gas is extracted via outlet 14. The overpressure on thegas inlet 15, vacuum level on the outlet 14 and geometry of the gap arearranged so that there is a high-velocity gas flow inwardly thatconfines the liquid. The force of the gas on the liquid between theliquid confinement structure 12 and the substrate W contains the liquidin a space 11. The inlets/outlets may be annular grooves which surroundthe space 11. The annular grooves may be continuous or discontinuous.The flow of gas is effective to contain the liquid in the space 11. Sucha system is disclosed in United States patent application publicationno. US 2004-0207824, which is hereby incorporated by reference in itsentirety. In another embodiment, the liquid confinement structure 12does not have a gas seal.

An embodiment of the invention relates to a particular type of extractorfor use in a fluid handling structure which substantially prevents themeniscus from advancing beyond a certain point. That is, an embodimentof the invention relates to a meniscus pinning device which pins theedge of liquid, e.g. in the form of a liquid meniscus, in a space 11between the final element of the projection system and the substrateand/or substrate table substantially in place. The meniscus pinningarrangement relies on the so-called gas drag extractor principle whichhas been described, for example, in U.S. patent application publicationno. 2008/0212046, which is hereby incorporated by reference in itsentirety. In that system the extraction holes may be placed in acornered shape. The corners are aligned with a direction of relativemotion between the projection system and the substrate and/or substratetable, for example the stepping and scanning directions. This helpsreduce the force on the meniscus between two outlets for a given speedin the direction of relative motion compared to a case where the twooutlets are aligned perpendicular to the direction of relative motion.However, an embodiment of the invention may be applied to a fluidhandling structure which, in plan, may have any shape, or to a fluidhandling structure that has a component part such as the extractionopenings arranged in any shape. Such a shape in a non-limiting list mayinclude an ellipse (such as a circle), a rectilinear shape (such as arectangle, e.g. a square, or parallelogram, e.g., a rhombus) or acornered shape with more than four corners (such as a four or morepointed star).

In a variation of the system of US 2008/0212046, to which an embodimentof the invention relates, the geometry of the cornered shape in whichthe openings are arranged allows sharp corners (selected from the rangeof about 60° to 90°, desirably the range of 75° to 90° and mostdesirably the range of 75° to 85°) to be present for the corners alignedboth in the preferred directions of relative motion, for example, in thescanning and in the stepping directions. This may allow increased speedin the direction of each aligned corner. This is because the creation ofliquid droplets due to an unstable meniscus in the scanning direction isreduced. Where corners are aligned with both the scanning and steppingdirections, increased speed may be achieved in those directions.Desirably the speed of movement in the scanning and stepping directionsmay be substantially equal.

FIG. 6 illustrates schematically and in plan the meniscus pinningfeatures of part of a fluid handling structure for use in an embodimentof the invention. The features of a meniscus pinning device areillustrated which may, for example, replace the meniscus pinningarrangement 14, 15, 16 of FIG. 5. The meniscus pinning device of FIG. 6comprises a plurality of discrete openings 50 arranged in a first lineor pinning line. Each of these openings 50 are illustrated as beingcircular though this is not necessarily the case. Indeed one or more ofthe openings 50 may be one or more selected from a circle, square,rectangular, oblong, triangular, an elongate slit, etc. Each openinghas, in plan, a length dimension (i.e. in the direction from one openingto the adjacent opening) of greater than 0.2 mm, desirably greater than0.5 mm or 1 mm, in an embodiment selected from the range of 0.1 mm to 10mm, in an embodiment selected from the range of 0.25 mm to 2 mm. In anembodiment the length dimension is selected from the range of 0.2 mm to0.5 mm, desirably the range of 0.2 mm to 0.3 mm. In an embodiment, thewidth of each opening is selected from the range of 0.1 mm to 2 mm. Inan embodiment, the width of each opening is selected from the range of0.2 mm to 1 mm. In an embodiment, the width of each opening is selectedfrom the range of 0.35 mm to 0.75 mm, desirably approximately 0.5 mm.

Each of the openings 50 of the meniscus pinning device of FIG. 6 may beconnected to a separate under pressure source. Alternatively oradditionally, each or a plurality of the openings 50 may be connected toa common chamber or manifold (which may be annular) which is itself heldat an under pressure. In this way a uniform under pressure at each or aplurality of the openings 50 may be achieved. The openings 50 can beconnected to a vacuum source and/or the atmosphere surrounding the fluidhandling structure or system (or confinement structure, barrier memberor liquid supply system) may be increased in pressure to generate thedesired pressure difference.

In the embodiment of FIG. 6 the openings are fluid extraction openings.The openings 50 are inlets for the passage of gas and/or liquid into thefluid handling structure. That is, the openings may be considered asoutlets from the space 11. This will be described in more detail below.

The openings 50 are formed in a surface of a fluid handling structure12. That surface faces the substrate and/or substrate table in use. Inone embodiment the openings are in a flat surface of the fluid handlingstructure. In another embodiment, a ridge may be present on the surfaceof the fluid handling structure facing the substrate. In an embodimentthe openings may be in the ridge. In an embodiment, the openings 50 maybe defined by needles or tubes. The bodies of some of the needles, e.g.,adjacent needles, may be joined together. The needles may be joinedtogether to form a single body. The single body may form the shape whichmay be cornered.

As can be seen from FIG. 7, the openings 50 are the end of a tube orelongate passageway 55, for example. Desirably the openings arepositioned such that they face the substrate W in use. The rims (i.e.outlets out of a surface) of the openings 50 are substantially parallelto a top surface of the substrate W. The openings are directed, in use,towards the substrate W and/or substrate table WT configured to supportthe substrate. Another way of thinking of this is that an elongate axisof the passageway 55 to which the opening 50 is connected issubstantially perpendicularly (within +/−450, desirably within 35°, 25°or even 15° from perpendicular) to the top surface of the substrate W.

Each opening 50 is designed to extract a mixture of liquid and gas. Theliquid is extracted from the space 11 whereas the gas is extracted fromthe atmosphere on the other side of the openings 50 to the liquid. Thiscreates a gas flow as illustrated by arrows 100 and this gas flow iseffective to pin the meniscus 90 between the openings 50 substantiallyin place as illustrated in FIG. 6. The gas flow helps maintain theliquid confined by momentum blocking, by a gas flow induced pressuregradient and/or by drag (shear) of the gas flow on the liquid.

The openings 50 surround the space to which the fluid handling structuresupplies liquid. That is, the openings 50 may be distributed around thesurface of the fluid handling structure facing the substrate and/orsubstrate table. The openings may be substantially continuously spacedaround the space (In an embodiment the spacing between some of theadjacent openings may be the same, although the spacing between adjacentopenings 50 may vary). In an embodiment, liquid is extracted all the wayaround the shape which may be cornered. Liquid is extractedsubstantially at the point at which it impinges on the shape. This isachieved because the openings 50 are formed all the way around the space(in the shape). In this way the liquid may be confined to the space 11.The meniscus may be pinned by the openings 50, during operation.

As can be seen from FIG. 6, the openings 50 may be positioned so as toform, in plan, a cornered shape (i.e. a shape with corners 52). In thecase of FIG. 6 the shape is a quadrilateral, such as a rhombus, e.g. asquare, with curved edges or sides 54. The edges 54 may have a negativeradius. An edge 54 may curve towards the center of the cornered shape,for example along a portion of the edge 54 located away from the corners52. However, the average of the angle of all points on the edge 54relative to a direction of relative motion may be referred to as a lineof average angle which may be represented by a straight line withoutcurvature.

Principal axes 110,120 of the shape may be aligned with the majordirections of travel of the substrate W under the projection system.This helps to ensure that the maximum scan speed is faster than if theopenings 50 were arranged in a shape in which the direction of movementis unaligned with an axis of the shape, for example a circular shape.This is because the force on the meniscus between two openings 50 may bereduced if the principle axes are aligned with a direction of relativemotion. For example, the reduction may be a factor cos θ. ‘θ’ is theangle of the line connecting the two openings 50 relative to thedirection in which the substrate W is moving.

The use of a square shape allows movement in the step and scanningdirections to be at a substantially equal maximum speed. This may beachieved by having each of the corners 52 of the shape aligned with thescanning and stepping directions 110, 120. If movement in one of thedirections, for example the scan direction, is preferred to be fasterthan movement in the other direction, for example the step direction,then the shape may be a rhombus. In such an arrangement the primary axisof the rhombus may be aligned with the scan direction. For a rhombicshape, although each of the corners may be acute, the angle between theline of average angle of two adjacent sides (or edges) of the rhombus,for example relative to a direction of relative motion in the steppingdirection, may be obtuse, i.e. more than 90° (for example selected fromthe range of about 90° to 120°, in an embodiment selected from the rangeof 90° to 105°, in an embodiment selected from the range of 85° to105°).

Throughput can be optimized by making the primary axis of the shape ofthe openings 50 aligned with the major direction of travel of thesubstrate (usually the scan direction) and to have another axis alignedwith the other major direction of travel of the substrate (usually thestep direction). It will be appreciated that any arrangement in which 9is different to 900 will give an advantage in at least one direction ofmovement. Thus, exact alignment of the principal axes with the majordirections of travel is not vital.

An advantage of providing the edges with a negative radius is that thecorners may be made sharper. An angle selected from the range of 75 to85° or even lower may be achievable for both the corners 52 aligned withthe scan direction and the corners 52 aligned with the step direction.If it were not for this feature then in order for the corners 52 alignedin both directions to have the same angle, those corners would have tohave 90°. If it was desired that a corner would have an angle of lessthan 90°, it would be necessary to select corners aligned with adirection of relative motion to be less than 90°. The other cornerswould have an angle of greater than 90°.

The openings may be arranged in a star shape. In an embodiment of a starshape, the edges are straight instead of curved. The edges may meet at apoint, e.g. an intermediate corner, which is radially inwardly of astraight line between two corners 52. This arrangement may not be assuccessful in pinning a meniscus at a high relative speed as anarrangement in which the edge between two adjacent corners 52 defined bythe line joining the openings is smooth. Such a line defined by theopenings 50 may define the cornered shape, is continuous and has acontinuously changing direction. In the star shape embodiment, theintermediate corner along the side of the shape may pin the meniscus.The sharper a corner, the more the forces pinning the meniscus arefocused on the corner. At a sharp corner, the pinning forces are focusedon a short length of the edge of the shape. A corner with a smoothercurve than a sharp corner, for example, a corner with a larger radius ofcurvature, has a longer length and so distributes the pinning forcesalong a longer curve of the corner i.e. around the corner. Thus, for acertain relative velocity between the substrate and the fluid handlingstructure, the effective meniscus pinning force applied to both cornersis the same. However, for a defined length of the edge, the effectivepinning force for the sharp corner is more than for the smoothly curvedcorner. The meniscus pinned at a sharp corner is more unstable at alower relative velocity between the substrate and the fluid handlingstructure than a meniscus pinned by the smoothly curved corner.

FIG. 7 illustrates that the opening 50 is provided in a lower surface 51of the fluid handling structure. This is however not necessarily thecase and the opening 50 may be in a protrusion from the lower surface ofthe fluid handling structure. Arrow 100 shows the flow of gas fromoutside of the fluid handling structure into a passageway 55 associatedwith the opening 50. Arrow 150 illustrates the passage of liquid fromthe space into the opening 50. The passageway 55 and opening 50 aredesirably designed so that two phase extraction (i.e. gas and liquid)desirably occurs in an annular flow mode. In annular gas flow gas maysubstantially flow through the center of the passageway 55 and liquidmay substantially flow along the wall(s) of the passageway 55. A smoothflow with low generation of pulsations results.

There may be no meniscus pinning features radially inwardly of theopenings 50. The meniscus is pinned between the openings 50 with dragforces induced by gas flow into the openings 50. A gas drag velocity ofgreater than about 15 m/s, desirably 20 m/s may be sufficient. Theamount of evaporation of liquid from the substrate may be reducedthereby reducing both splashing of liquid as well as thermalexpansion/contraction effects.

A plurality of discrete needles (which may each include an opening 50and a passageway 55), for example at least thirty-six (36), each with adiameter of 1 mm and separated by 3.9 mm may be effective to pin ameniscus. In an embodiment, 112 openings 50 are present. The openings 50may be square, with a length of a side of 0.5 mm, 0.3 mm, 0.2 mm or 0.1mm.

Other geometries of the bottom of the fluid handling structure arepossible. For example, any of the structures disclosed in U.S. patentapplication publication no. US 2004-0207824 could be used in anembodiment of the invention.

As can be seen in FIG. 6, an elongate aperture 61 (which may be slitshaped) is provided outside the openings 50. The elongate aperture 61may be located further away from the space containing the immersionfluid than the openings 50 arranged in the first line. The aperture 61may be substantially parallel to the first line in which the openings 50are arranged. The elongate aperture may form a second line or knifeline. The second line may surround the periphery of the shape formed bythe openings 50. In an embodiment the elongate aperture is continuousand may completely surround the shape formed by the first line. In use,the aperture 61 is connected to an over pressure source. Gas flowingfrom the aperture 61 may form a gas knife 60 surrounding the meniscuspinning system formed by openings 50. The function of this gas knifewill be described below. In an embodiment the elongate aperturecomprises a plurality of discrete apertures (which may be elongate)along a side 54 of the shape. The plurality of apertures may be arrangedin series.

In an arrangement, a liquid handling device may be as describedhereinabove but lacks the gas knife 60. In such an arrangement, when thesubstrate table WT moves so that the meniscus of the immersion liquidcrosses a lyophilic region, or a region of relatively low lyophobicity(i.e. having a lower contact angle to the immersion liquid than otherparts of the substrate or substrate table surface), the immersion liquidmay spread out into a film over the region of low lyophobicity. In thepresence of water reference to lyophobicity is to hydrophobicity andlyophilic is to hydrophilic.

Formation of a film may depend on whether the speed of relative movementof the liquid meniscus and substrate or substrate table (“scan speed”)is greater than a critical speed. With respect to a meniscus pinned bythe openings 50, the critical speed is the relative velocity between thefluid handling structure 12 and the facing surface of a substrate and/orsubstrate table above which the meniscus may be no longer stable. Thecritical speed depends on the properties of the facing surface. Thehigher the contact angle of the facing surface the higher the criticalspeed in general. Once a film has begun to form, it may continue to groweven if the substrate has now moved so that the meniscus is over an areawith a higher contact angle. For such an area with higher contact angle,the critical speed is higher. If the substrate moves at critical speedof the area with which the meniscus was previously in contact (i.e. alower contact angle), the scan speed may be lower than the currentcritical scan speed.

The film may, in some cases after a short delay, break up into largedroplets which are undesirable. In some cases, subsequent movements ofthe substrate table may cause the droplets to collide with the meniscus,which may generate bubbles in the immersion liquid. Regions having arelatively low lyophobicity (e.g. in the presence of waterhydrophobicity) may include the edge of the substrate, a removablefeature (e.g. an adherable planar member such as a sticker) on thesubstrate table, a positioning feature (e.g. an encoder grid oralignment mark) and/or a sensor (e.g. a dose sensor, an image sensor ora spot sensor). In an embodiment a region of relatively low lyophobicity(e.g. in the presence of water hydrophobicity) may be formed bydegradation of a coating or surface treatment. The coating or surfacetreatment may be provided to increase the lyophobicity (e.g. in thepresence of water hydrophobicity) of the surface on which it isprovided.

In an embodiment, the gas knife 60 may function to reduce the thicknessof any liquid film left on the substrate or substrate table. Reducingthe thickness of the film may reduce the likelihood that it breaks intodroplets. Additionally or alternatively the gas flow from the gas knife60 may drive liquid towards the openings 50 and be extracted.

In an embodiment, the gas knife 60 operates to reduce the formation of afilm. To achieve this, it is desirable that the distance between thecenter lines of the gas knife aperture 61 and the meniscus pinningopening 50 is selected from the range of from 1.5 mm to 4 mm, desirablyfrom 2 mm to 3 mm. (In an embodiment, the gas knife aperture 61 has aplurality of apertures 61). The second line along which the aperture 61is arranged generally follows the first line along which the openings 50are formed so that the distance between adjacent ones of the aperture 61and opening 50 is within the aforementioned ranges. The second line maybe parallel to the line of the openings 50, although this notnecessarily the case as described in U.S. Patent Application PublicationNo. US 2010-0313974, which is hereby incorporated by reference in itsentirety.

It may desirable to maintain a constant separation between adjacentapertures 61 (where a plurality of apertures is present along the secondline) and adjacent openings 50. In an embodiment this is desirable alongthe length of the center lines of the apertures 61 and openings 50. Inan embodiment the constant separation may be in the region of one ofmore corners of the fluid handling device.

In arrangements such as those discussed above with reference to FIGS. 6and 7, immersion liquid droplets may escape from the space in which theimmersion liquid is confined during relative movement under the spaceof, for example, a height step in the surface facing the space. This mayoccur, for example, at a gap between an edge of a substrate and an edgeof a recess in the table supporting the substrate, or at the surface ofa sensor. Escape of liquid droplets may in particular occur when therelative speed between the fluid handling structure and the facingsurface, e.g. scanning speed, is larger than a critical speed. Such arelative speed might be necessary when a higher scanning speed orthroughput is desired. Such a critical speed may be dependent on atleast one property of the facing surface.

In escaping from the immersion liquid in the space 11, the dropletbreaks from a meniscus of the immersion liquid between the fluidhandling structure and a facing surface (such as a substrate or asubstrate table which supports the substrate). The meniscus may bepinned to the fluid handling structure by a fluid extraction openingwhich may extract liquid and gas in a two phase fluid flow, as discussedabove. The droplet may escape from a trailing side of the immersionspace with respect to the movement of the facing surface.

In moving with the facing surface (with respect to the fluid handlingstructure) the droplet may then encounter a gas knife which directs thedroplet back to the liquid extractor. However, sometimes the conditionsmay be such that the droplet is blocked from moving further away fromthe meniscus by the gas knife. Sometimes such a droplet may pass beyondthe gas knife. In an embodiment the droplet escapes the influence of acomponent of the fluid handling structure. In another embodiment, thedroplet encounters a further extractor and gas knife which may serve toextract and/or block the movement of the droplet away from the meniscus.

When the relative motion between the fluid handling structure and thefacing surface in the plane of the facing surface, e.g. the scanning orstepping direction is subsequently changed, such a droplet can moverelative to the fluid handling structure back towards the liquidmeniscus. The droplet may at least partly be stopped by a gas knife itfirst passed when escaping from the meniscus. The droplet may besufficiently large that it passes the gas knife towards the meniscus.The droplet may be extracted by extraction through the extractionopening provided at or at least near the edge or boundary of theimmersion liquid confined in the space. However, if such a droplet isnot extracted completely it may create a bubble on collision with theliquid meniscus of the liquid confined in the space.

The droplet may be insufficiently large and/or have insufficientrelative speed to pass the gas knife towards the meniscus. The dropletmay merge with one or more droplets which may be small to form a biggerdroplet in front of the gas knife. In this case, the gas knife may beoverloaded with immersion liquid, allowing the merged droplet to pass.Such a droplet will move relative to the fluid handling structuretowards, and potentially collide with, the meniscus and may potentiallycreate one or more bubbles.

In an embodiment, a significant reduction of the (amount and) size ofthe droplets passing a gas knife towards a meniscus during a change inthe scanning direction may be achieved by adding an extra extraction 300very close to the gas knife, as shown, for example, in FIG. 8, which issimilar to FIG. 7 but with the addition of extraction 300. Theextraction may be located adjacent the opening of the gas knife 61, awayfrom the immersion space 11. It will be appreciated that variations ofthe arrangement depicted in FIG. 7 discussed herein may also be appliedto the embodiment depicted in FIG. 8.

The extra extraction may prevent saturation (or breaching) of the gasknife. Therefore, the gas knife may retain its effectiveness in blockinga droplet from reaching the meniscus (i.e. its desired droplet stoppingpower). For example, the extra extraction may remove the immersionliquid that the gas knife collects (or “bulldozers”) when a change inthe scanning direction is made. The amount of immersion liquid beingextracted may be very little but sufficient to prevent overloading thegas knife. In this situation the gas knife may have to “bulldozer” theimmersion liquid, or push the collected immersion liquid. This mayrequire the gas knife flow to be larger than the flow through theextraction at the edge of the space containing the immersion liquid. Theprovision of the extra extraction 300 may prevent this situation, suchthat the gas knife flow does not have to be as large, as compared, forexample, to an arrangement without the extra extraction.

The extra extraction 300 may be provided by an elongate opening or aplurality of openings 302 adjacent a gas knife device that is used inconjunction with the extraction at the edge of the space containing theimmersion liquid. For example, the one or more openings 302 of the extraextraction may be adjacent the elongate aperture 61 of the gas knife 60.The separation between the two lines of openings used for the extractionand the line of the gas knife device may be substantially the same atall locations around the space containing the immersion liquid.

As shown in FIG. 9, the edge 301 of the opening 302 for the extraextraction 300 adjacent the gas knife device that is closest to the gasknife device 60 may be provided at an oblique angle α relative to thesurface 51 of the fluid handling structure 12 that is between the firstand second lines and beyond the opening adjacent the gas knife device.In this arrangement, the width of the opening adjacent the gas knifedecreases with distance from the surface.

In an embodiment, the angle α of the edge 301 of the opening 302relative to the surface 51 of the fluid handling structure 12 isselected from the range of from 10° to 60°, or from 10° to 45°, or isdesirably 20°. The provision of an angled edge 301 of the opening 302for the extra extraction 300 may be beneficial because it enables theedge of the opening 302 to be as close as possible to the edge of theaperture 61 of the gas knife device 60. However, at the same time, itmay be ensured that the thickness of the wall 303 separating theaperture 61 from the channel providing the extra extraction 300 is notso thin that additional manufacturing challenges are created.

The separation of the nearest edges of the elongate aperture 61 of thegas knife device 60 and the elongate opening or plurality of openings301 for the additional extraction 300, namely adjacent the gas knifedevice 60, may be selected from the range of from 0.25 mm to 0.75 mm,desirably 0.5 mm. In general, the one or more openings of the additionalextraction 300 may be as close as possible to the aperture 61 of the gasknife device 60. This may minimize the size of liquid droplets that maybe formed by the merger of smaller droplets adjacent the gas knife. Inturn, this may reduce the size of droplets that may pass through the gasknife 60, reducing the likelihood of bubbles forming in the immersionliquid when the droplets collide with the meniscus. However, as notedabove, the desire to minimize the separation must be balanced with thedifficulties that may be introduced in the process of manufacturing thefluid handling structure 12 if the wall 303 separating the openings ofthe extra extraction 300 from the aperture 61 of the gas knife device 60becomes too small.

The width of the opening 302 of the extra extraction 300 may, forexample, be selected from the range of from 30 μm to 200 μm, or from 100μm to 150 μm.

In embodiments as depicted in FIGS. 7 and 8, a controller 63 is providedto control the rate of flow of gas through the aperture 61 in the secondline to form the gas knife 60. In an embodiment, the controller 63 mayalso control the rate of flow of gas through the openings 50 in thefirst line. The controller 63 may control an over pressure source 64(e.g. a pump) and/or an under pressure source 65 (e.g. a pump, possiblythe same pump that provides the overpressure). The controller 63 may beconnected to one or more suitable flow control valves in order toachieve the desired flow rates. The controller may be connected to oneor more two phase flow rate meters associated with one or more openings50 to measure the extracted flow rate, a flow rate meter associated withthe aperture 61 to measure the supplied gas flow rate, or both. Asuitable arrangement for a two phase flow meter is described in U.S.Patent Application Publication No. US 2011-0013159, which is herebyincorporated by reference in its entirety.

In an embodiment, as depicted in FIG. 8, the one or more openings 302 ofthe extra extraction 300 may be connected to an under pressure source305 (e.g. a pump, possibly the same as provides one or both of the overpressure source 64 and the under pressure source 65). As shown in FIG.8, the under pressure source 305 for the additional extraction 300 maybe controlled by the same controller 63 as is used to control theoverpressure source 64 and/or the under pressure source 65. Likewise thecontroller 63 may be connected to one or more suitable flow controlvalves and/or flow rate meters as above in order to achieve desired flowrates. It will also be appreciated that separate controllers may beprovided for one or more of the under pressure and over pressure sources64,65,305.

In an embodiment, the controller 63 is configured such that the flowrates of the gas knife 60 from the elongate aperture 61 and theextraction through the one or more openings 50 and the one or moreopenings 302 of the extra extraction 300 are such that the flow of gasfrom the gas knife device 60 is substantially perpendicular to thesurface of the fluid handling structure between the first and secondline. This may be achieved, for example, by balancing the extractionrate through the one or more openings 50 in the first line and the oneor more openings 302 of the extra extraction 300 and balancing the totalextraction with the gas flow of the gas knife device 60.

Controlling the gas flow rates such that the flow of gas from the gasknife device 60 is perpendicular, or relatively perpendicular, to thesurface of the fluid handling structure, and therefore the opposingsurface of the substrate table WT and/or substrate W may improve theperformance of the gas knife device for a given gas flow rate of the gasknife device. This in turn may increase the scan rate that may be used.

In an arrangement, the gas flow rate out of the aperture 61 in thesecond line to form the first gas knife device 60 may be less than areequal to 100 liters per minute, for example 75 liters per minute orless. The gas flow rate extracted through the one or more openings 50 inthe first line may be less than or equal to 75 liters per minute, forexample 50 liters per minute. The gas flow rate of the additionalextraction 300 may be, for example, higher because it will only beextracting small quantities of liquid. For example, the gas flow rate ofthe additional extraction 300 may be approximately 75 liters per minute.

The gas knife is desirably close enough to the openings 50 to create apressure gradient across the space between them. There is desirably nostagnant zone in which a layer of liquid (i.e. a liquid film), or aliquid droplet can accumulate, for example beneath the fluid handlingstructure 12. In an embodiment, the flow rate of gas through theopenings 50 may be coupled to the gas flow rate through the elongateaperture 61 as described in U.S. Patent Application Publication No. US2010-0313974 and U.S. Patent Application Publication No. US2007-0030464, which are each hereby incorporated by reference in itsentirety. The gas rate may therefore be directed substantially inwardlyfrom the aperture 61 to the openings 50. Where the gas flow rate throughthe openings 50 and the aperture 61 is the same, the flow rate may bereferred to as ‘balanced’. A balanced gas flow may be desirable whenscanning in one direction as it minimizes the thickness of a liquidresidue, e.g. film.

In an embodiment, the gas flow rate through the openings 50 in the firstline and the aperture 61 in the second line may be balanced on one sideof the fluid handling structure 12 when scanning in a first direction,in which the surface opposite the fluid handling structure is travelingaway from the meniscus. When traveling in the opposite direction, thegas flow rate of the gas knife 60 may be balanced with the sum of theextraction gas flow rate through the openings 50 in the first line andthe extra extraction 300.

As described elsewhere herein, the openings 50 may be arranged to formany closed shape which may include in a non-limiting list, e.g. aquadrilateral such as a parallelogram, a rhombus, a rectangle, a square,or ellipse such as a circle. In each case the aperture 61 for the gasknife 60 may have a substantially similar shape as the shape formed bythe openings 50. In an embodiment of the invention, an elongate openingmay be provided in the first line in place of the plurality of openings50 for use in extracting liquid from the space into the fluid handlingstructure. The separation between the edge of the shape formed by theone or more openings 50 and the shape formed by the aperture 61 iswithin the aforementioned ranges. In an embodiment the separation isdesirably constant.

In general, it will be appreciated that in an embodiment, thearrangement of the fluid handling structure 12 may be configured inorder to ensure that the performance of the extra extraction 300 is ashigh as possible or maximized, namely it is effective at extractingliquid adjacent the gas knife 60. As discussed above, this may beachieved by ensuring that the extraction fluid flow through the extraextraction 300 is sufficiently high. Alternatively or additionally, thismay be achieved by ensuring that the additional extraction 300 is asclose as possible to the edge of the aperture 61 of the gas knife device60. Alternatively or additionally, this may be achieved by ensuring thatthe gas flow through the gas knife device 60 is sufficiently high thatthere is a radial flow of gas outwards, namely in the direction of theextra extraction 300. Alternatively or additionally, this may beachieved by operating the fluid handling structure 12 at a fly heightthat is as low as possible, taking into account other limitations of theoperation of the fluid handling structure and the lithographicapparatus, namely ensuring that the lower surface 51 of the fluidhandling structure 12 is as close as possible to the surface of thesubstrate W and/or substrate table WT.

FIG. 10 schematically depicts in cross-section a part of a fluidhandling structure that is a development of the arrangement depicted inFIG. 7. At the boundary between the space 11 in which the liquid iscontained and a region that is external to the fluid handling structure,for example in the ambient atmosphere external to the fluid handlingstructure, one or more openings 50 and the aperture 61 may be arrangedin the manner discussed above. One or more openings 50 may be arrangedin a first line for use in extracting liquid from the space into thefluid handling structure. The aperture 61 may be provided in a secondline and arranged to form a gas knife device. The gas from the gas knifemay force liquid towards the openings 50 in the first line.

One or more openings 71 may be provided in a third line, or dropletline, further away from the immersion liquid than the first and secondlines. A second gas knife device is formed by an aperture 72 arranged ina fourth line, or droplet knife line. (In an arrangement, the aperture72 has a plurality of apertures 72). The fourth line is arranged to befurther from the space 11 containing the immersion liquid than the thirdline. The gas flow through the second gas knife device may be mainlydirected inwardly so that most of it passes through the openings 71. Inan arrangement the gas flow through the one or more openings 71 and theaperture 72 of the second gas knife device is balanced.

The fluid handling structure of this arrangement includes a first gasknife device operating in conjunction with a first plurality of openings50. This combination performs the primary extraction of immersionliquid.

The fluid handling structure has a second gas knife device operatingwith the third line of openings 71. The provision of an additionalcombination of one or more openings and associated gas knife has beenfound to be unexpectedly beneficial.

An arrangement such as that depicted in FIG. 7, with a single gas knifedevice and a single associated line of openings, may leave a residue ofliquid on the surface of the substrate W and/or substrate table WT. Theliquid residue may be in the form of a liquid film or a plurality ofdroplets. After a while, the film may break up into a plurality ofdroplets. The droplets may grow into larger droplets and may becomeunacceptably large. The liquid residue may be left, as explained herein,when the scan speed exceeds the critical scan speed for a portion of thefacing surface. This may, for example, occur when the scan speedincreases for a surface with a continuous contact angle beyond thecritical scan speed for the surface. The liquid residue may be left inthe location of a portion of a surface where the contact angle changesso the critical scan speed for that portion decreases so the scan speedexceeds the critical scan speed, even if the scan speed is constant.Such a portion may be an edge of a feature, such as the edge of thesubstrate, a shutter member, a sensor or a sensor target, for example atthe moment when the liquid meniscus crosses the edge.

In arrangements in which the gas knife device is decoupled from the lineof openings 50, 71 by a connection to atmospheric pressure, for exampleby a space that is connected to atmosphere and is located between thegas knife device and the openings 50, 71, further problems may occur.Liquid may accumulate between the gas knife device and the openings,creating large droplets. When the direction of movement from thesubstrate W and/or substrate table WT relative to the projection systemPS and the fluid handling structure changes, such large droplets maycollide with the advancing meniscus of the immersion liquid. Thecollision of a droplet with the meniscus may cause an inclusion of gas,creating a bubble which may be small or larger. Furthermore, adisturbance of the meniscus caused by the collision may also form abubble. Formation of a bubble is undesirable. An arrangement asdescribed herein may help reduce one or more of the above or otherproblems.

The provision in the fluid handling structure of two gas knife devicesand associated openings for extraction permits the design and/or settingof process control parameters of each combination to be selected for thespecific purpose of each combination, which may be different. The gasflow rate out of the aperture 61 in the second line, forming the firstgas knife, may be less than the gas flow rate out of the aperture 72 inthe fourth line forming the second gas knife device.

In an arrangement it may be desirable for the gas flow rate for thefirst gas knife device to be relatively low because, as explained above,the flow through the plurality of openings 50 in the first line is intwo phase, with a significant amount of liquid. If the flow rate throughthe aperture 61 in the second line and the plurality of openings 50 inthe first line is an unstable two phase flow regime, for example theflow rate may be too high, the two phase flow may result in forcevariations, e.g. vibrations, which is undesirable. On the other hand,the more stable the flow regime, for example the lower the flow rate,through the aperture 61 in the second line and/or the plurality ofopenings 50 in the first line, the greater the leakage of immersionliquid past the gas knife device at a given speed of movement of thesubstrate W and/or substrate table WT relative to the projection systemPS and the fluid handling structure. Therefore, the gas flow rate in asingle gas knife arrangement was essentially a compromise between thesetwo conflicting demands.

The provision in the fluid handling structure of the second gas knifedevice and associated extraction beneficially enables a lower flow rateto be used for the first gas knife device. The second gas knife devicemay be used to remove droplets of liquid that pass beyond the first gasknife device. Furthermore, the gas flow rate through the aperture 72 inthe fourth line and the one or more openings 71 in the third line may berelatively high. This is because the flow is largely gas. Beneficially,this increased flow rate improves the performance of removal of liquiddroplets from the surface of the substrate W and/or the substrate WT.

In an arrangement, the gas flow rate out of the aperture 61 in thesecond line to form the first gas knife device may be less than or equalto 100 liters per minute, desirably less than or equal to 75 liters perminute, desirably approximately 50 liters per minute or less. In aparticular arrangement, the gas flow rate out of the aperture 72 in thefourth line to form the second gas knife device may be greater than orequal to 60 liters per minute, desirably greater than or equal to 100liters per minute, desirably approximately 125 liters per minute ormore.

Although an arrangement such as that depicted in FIG. 10 maybeneficially reduce the liquid that may accumulate between the one ormore openings 50 in the first line and the one or more openings 71 inthe third line, it may not eliminate the accumulation of such liquid.Accordingly, a fluid handling structure as schematically depicted inFIG. 11 may be provided in an embodiment of the invention. As depicted,the arrangement corresponds to that depicted in FIG. 10 but includesadditional extraction 300 adjacent to the elongate aperture 61 of thefirst gas knife device 60. As with the arrangement depicted in FIG. 8,the additional extraction 300 may prevent large droplets of liquid fromaccumulating adjacent the first gas knife device 60, in particular whenthe direction of scanning of the substrate table WT and/or substrate Wrelative to the fluid handling structure is reversed. Variations of thearrangements discussed above in relation to FIGS. 8 and 10 apply to thearrangements including the additional extraction 300 as depicted in FIG.11.

A controller 73 (which may be the same as the controller 63 discussedabove) is provided to control the rate of flow of gas through theaperture 72. The controller 73 also controls the rate of flow of gasthrough the one or more openings 71. The controller 73 may control anoverpressure source 74 (e.g. a pump) and/or an underpressure source 75(e.g. a pump, possibly the same pump as provides the overpressure).There may be one or more suitable control valves connected to andcontrolled by the controller 73 in order to provide the desired flowrates. The controller may control the valves based on flow measurementssupplied by one or more two phase flow meters arranged to measure theflow through the one or more openings 71, one or more flow metersarranged to measure the flow through the aperture 72, or both. Such anarrangement may be similar to the arrangement for the flow componentsassociated with the first and second lines.

One or both of the controllers 63,73 may be configured to control thegas flow through the openings 50,302,71 in proportion to the gas flowrate of the associated gas knife. In an embodiment, the gas flow ratethrough the gas knife is up to 20% or up to 10% different from the totalflow rate through the associated openings 50,302,71. In an embodimentthe gas flow rate through openings 50,302,71 may be controlled to matchthe gas flow through the associated one or more apertures 61,72. In anembodiment, the gas flow rate through the elongate aperture 72 of thesecond gas knife may match, for example, be substantially the same as,the gas flow rate through the opening 71. Similarly, the gas flow ratethrough the elongate aperture 61 of the first gas knife 60 may match thegas flow rate through one or both sets of the openings 50,302 on eitherside on the first gas knife 60, as discussed above in relation to thediscussion of the arrangement depicted in FIG. 8.

It will be appreciated that the arrangement of the embodiments of theinvention depicted in FIGS. 8, 9 and 11, may include several variations.

In an embodiment, the controllers 63,73 may control the activation ofeither or both gas knives such that it is active when it is, or may be,required. In other words, the gas knife may be switched off underappropriate predetermined conditions. For example, the gas knife may beswitched off when the scan speed is safely below a critical speed and isswitched on when the scan speed goes above, or is likely to go above,the critical speed for the surface currently under the meniscus orapproaching the meniscus. For example, when a central portion of thesubstrate moves under the fluid handling structure 12, one or both ofthe gas knives may be switched off. The contact angle is constant overthis portion of the substrate and the critical scan speed for theportion may be sufficiently high that it is not exceeded. Before, duringand/or after the meniscus of the space moves over an edge, for exampleof the substrate, sensor, shutter member or sensor target, one or bothof the gas knife devices may be operational.

The third and fourth lines, along which the one or more openings 71 andthe aperture 72 may be arranged, may generally follow the first andsecond lines along which the one or more openings 50 and the aperture 61are formed. In an embodiment the shape formed by the one or moreopenings 71 is different from the shape formed by the one or moreopenings 50. It may be desirable for the third and fourth lines, e.g. inan embodiment the first to fourth lines, to be parallel such that thereis a constant separation between the lines.

In an embodiment, the aperture 72 in the fourth line, used to form thesecond gas knife device where desired may have the same features asdescribed with reference to the aperture 61 in the second line. As withthe aperture 61 of the first gas knife device, the aperture 72 may beformed as a single slit or as a plurality of elongate apertures.

The one or more openings 71 in the third line where required may beformed as a single elongate slit or as a plurality of elongate openings.

In an embodiment, the lower surface 51 of the fluid handling structuremay be arranged such that an outer portion 51 a of the lower surfaceextends away from the aperture 72 in the fourth line.

In the embodiment depicted in FIGS. 10 and 11, a recess 80 having adepth of D1 is provided in the lower surface 51 of the fluid handlingstructure. The recess 80 may be provided in a fifth line, or a recessline, between the second and third lines. In an embodiment, the recess80 is arranged such that it is parallel to any of the first to fourthlines, desirably at least the second line, the third line or both.

The recess 80 may include one or more openings 81 connected by a gasconduit 82 to atmosphere, such as the ambient atmosphere, for example toa region external to the fluid handling structure. The recess 80,desirably when connected to an external atmosphere, may function todecouple the first gas knife device and associated one or more openings50 in the first line from the second gas knife device and associated oneor more openings 71 in the third line. The recess 80 decouples theoperation of the components located either side; so the featuresradially inward of the recess are decoupled from the features radiallyoutward.

On either side of the recess 80, there may be respective portions 51b,51 c of the lower surface 51 of the fluid handling structure. Therespective portions 51 b, 51 c may respectively separate the edge of therecess 80 from the edge of the one or more openings 71 in the third lineand the aperture 61 in the second line. (Note that these edges ofaperture 61 and one or more openings 71 are not the second and thirdlines, because the lines pass through the center of the cross-sectionsof the openings; the edges are therefore away from the line.) Theportions 51 b,51 c of the lower surface 51 of the fluid handlingstructure on either side of the recess 80 may, in conjunction with thesurface of the substrate W and/or the substrate table WT, function asrespective dampers. Such a damper may assist in ensuring that the gasflows from the first and second gas knives flow towards the respectiveopenings 50,71. In an embodiment one or both of the surfaces 51 b, 51 cmay function as a damper.

In order to help reduce the likelihood of liquid collecting within therecess 80, the recess may be provided with a shape without a sharp edge.The surface may be smoothly rounded. A sharp edge is undesirable becauseliquid may easily collect. For example, the shape of the recess 80 maybe configured such that the minimum radius of curvature at any pointaround the surface of the recess is at least 0.1 mm, desirably greaterthan 0.2 mm.

In an embodiment, a fluid handling structure may include one or moreopenings in the lower surface 51 of the fluid handling structure that isconnected by a gas conduit to atmosphere, such as the ambientatmosphere, for example to a region external to the fluid handlingstructure. For example, such openings connected to atmosphere may beprovided to an embodiment that does not incorporate a recess such asthat described above. Such an arrangement may be used to decouple thefirst gas knife and associated one or more openings 50 in the first linefrom the second gas knife device and associated one or more openings 71in the third line.

As discussed above, liquid collecting on the lower surface 51 of thefluid handling structure, in particular between the aperture 61 in thesecond line and the one or more openings 71 in the third line, may beundesirable. The collected liquid may cause problems when the directionof relative movement of the substrate W and substrate table WT withrespect to the projection system and the fluid handling structurechanges. In an embodiment, a lithographic apparatus that includes afluid handling structure described herein may include a controller PWCthat is arranged to control the actuator system of a positioner PWconfigured to move the substrate table WT and a substrate W heldthereon.

The controller PWC may be configured such that if the speed of thesubstrate table WT relative to the projection system PS is above aparticular velocity, steps are taken to reduce the problems that may becaused by the collected liquid as discussed above. The speed may beselected to correspond to a critical velocity of the first gas knifedevice for example with respect to a portion of the facing surface, orslightly below this critical velocity. The critical velocity may beconsidered as a velocity of the substrate table WT relative to theprojection system PS at which immersion liquid leakage through the gasknife, for example radially outwards, exceeds a given amount. It will beappreciated that such a critical velocity may be dependent on theconfiguration of the gas knife device, the gas flow rate of the gasknife device and/or the nature of the surface of the substrate and/orsubstrate table WT at that point.

The speed of the substrate table WT relative to the projection system PSmay be above the given speed. It may be required to change the directionof movement of the substrate table relative to the projection system. Inan embodiment, the controller PWC is configured such that if the speedis above the given speed and it is required to change direction of themovement of the substrate table, the controller PWC first reduces thespeed of the substrate table relative to the projection system PS belowthe given speed. The controller PWC may then initiate the change ofdirection. Accordingly, the change of direction no longer occurs above,for example, the critical velocity of the first gas knife device,minimizing or reducing the problems caused by immersion liquid that mayhave collected between the first and second gas knife devices.

FIG. 12 depicts a fluid handling structure according to an embodiment ofthe invention. As shown, the fluid handling structure of this embodimentis similar to the fluid handling structure depicted in FIG. 11. However,in this embodiment no recess connected to atmosphere is provided.Instead, the lower surface 51 of the fluid handling structure iscontinuous between the aperture 61 forming the first gas knife deviceand the one or more openings 71 in the third line. In other words, inthis region, there is no opening or aperture in the lower surface 51 ofthe fluid handling structure 12.

In this embodiment, the gas flow through the aperture 61 in the secondline may be balanced with the gas flow through the one or more openings50 in the first line and the gas flow through the additional extraction300. The gas flow through the aperture 72 in the fourth line may bebalanced with the gas flow through the one or more openings 71 in thethird line. It is therefore not necessary to decouple these arrangementsradially inward and radially outward of the lower surface 51.Beneficially, therefore, the recess 80 of FIG. 11 is not required,reducing the likelihood of liquid collecting in the space between theaperture 61 in the second line and the one or more openings 71 in thethird line or reducing the amount of liquid that is collected in thisregion. In this case, the separation between the aperture 61 in thesecond line and the one or more openings 71 in the third line may beselected from the range of from 1 mm to 4 mm, for example 2 mm.

FIG. 13 depicts a fluid handling structure according to an embodiment ofthe invention. As shown, the fluid handling structure of this embodimentis similar to the fluid handling structure depicted in FIG. 11. Forbrevity, the differences between the embodiments will be discussed andit will be appreciated that the variants discussed above in relation tothe embodiment depicted in FIG. 11 may also apply to the embodimentdepicted in FIG. 13.

As shown in FIG. 13, the lower surface 151 of the fluid handlingstructure 12 may be arranged such that, in use, the separation betweenthe different parts 151 a,151 b,151 c of the lower surface 151 and theupper surface of the substrate W and/or substrate table WT are not thesame. In an embodiment as depicted, there is a separation D2 between aportion 151 c of the lower surface 151 in the region of the openings 50in the first line, the aperture 61 of the gas knife device 60 in thesecond line and the openings 302 of the extra extraction and thesubstrate W and/or substrate table WT. There may be a separation D3between portions 151 a,151 b of the lower surface adjacent to the one ormore openings 71 in the third line and the aperture 72 in the fourthline and the substrate W and/or substrate table WT.

The separation D2 may be greater than the separation D3. This is incontrast to the embodiment depicted in FIG. 11, in which the lowersurface 51 of the fluid handling structure is generally planar. Thelower surface may be planar except for the provision of the openings50,302,71 and apertures 61,72 in the first to fourth lines and therecess 80. Accordingly, for the embodiment of FIG. 11, the separation ofeach part of the lower surface 51 around the openings 50,302,71 andapertures 61,72 in the first to fourth lines from the upper surface ofthe substrate W and/or substrate table WT is substantially the same. Inanother embodiment the separation D3 may be greater than the separationD2.

An arrangement such as that depicted in FIG. 13, namely one withdifferent distances between a facing surface and the lower surface 151,may be beneficial because various factors affect the optimum separationbetween the lower surface 151 of the fluid handling structure 12 and theupper surface of the substrate W and/or substrate table WT. For example,it may be desirable for the separation between the lower surface 151 ofthe fluid handling structure around the one or more openings 50 in thefirst line and the upper surface of the substrate W and/or substratetable WT to be as large as possible. This may reduce or minimize theprobability of bubbles forming when a droplet collides with themeniscus. This situation may occur, for example, during a change in thescanning direction of the substrate W and/or substrate table WT.

However, it may be desirable to minimize the separation between thelower surface 151 of the fluid handling structure 12 around the aperture72 in the fourth line that is used to form the second gas knife. Forexample, the smaller the separation, the lower the flow rate that may berequired and/or the wider the aperture 72 may be in order to provideeffective drying.

Therefore, the lower surface 151 of the fluid handling structure 12 maybe arranged such that the separation of the lower surface 151 around thefirst line from the upper surface of the substrate W and/or substratetable WT is different from the separation of the lower surface 151around the fourth line from the upper surface of the substrate W and/orsubstrate table WT. It is therefore possible to improve the performanceof both parts of the fluid handling structure rather than selecting asingle or substantially constant separation between all parts of thelower surface 151 and the upper surface of the substrate W and/or thesubstrate table WT. The need to compromise between the two conflictingrequirements may be avoided.

In an embodiment the separation between the lower surface 51; 151; 251of the fluid handling structure 12 of any of the embodiments of thepresent invention and the upper surface of the substrate W and/or thesubstrate table WT may be selected from the range of 50 μm to 250 μm.

In an embodiment such as that depicted in FIG. 13, the separation D2between the lower surface 151 around the one or more openings 50 in thefirst line and the upper surface of the substrate W and/or substratetable WT may be selected from the range of 130 μm to 250 μm, or therange of 180 μm to 250 μm, desirably approximately 230 μm. In anembodiment such as that depicted in FIG. 13, the separation D3 betweenthe lower surface 151 adjacent to the aperture 72 in the fourth lineused to form the second gas knife and the upper surface of the substrateW and/or substrate table WT may be selected from the range of 50 μm to180 μm, desirably approximately 130 μm.

It will be appreciated, however, that the optimum separations betweenthe different parts of the lower surface 151 of the fluid handlingstructure and the upper surface of the substrate W and/or substratetable WT may be dependent upon the nature of the upper surface of thesubstrate W and/or substrate table WT. For example, a relevant factormay be, in a non-limiting list: the receding contact angle with theliquid, the scan speed of the substrate W and/or substrate table WT andthe flow rate of at least one of the gas knife devices.

As noted herein, it may be desirable to optimize, for example, maximizethe separation D2 between the lower surface 151 around the one or moreopenings 50 in the first line and the upper surface of the substrate Wand/or substrate table WT. However it should further be appreciated thatthere may be a maximum practical separation. Beyond the optimum, forexample maximum, practical separation that may be used, the leakage ofliquid may become excessive.

As depicted in FIG. 13, the separation of the lower surface 151 of thefluid handling structure 12 around the aperture 61 in the second line(used to form the first gas knife 60) and the openings 302 of the extraextraction 300 from the upper surface of the substrate W and/orsubstrate table WT may be the same as the separation of the lowersurface 151 around the one or more openings 50 in the first line fromthe upper surface of the substrate W and/or the substrate table WT.However, it should be appreciated that this need not be the case.

As depicted in FIG. 13, the separation between the lower surface 151 ofthe fluid handling structure 12 adjacent to the aperture 72 in thefourth line (used to form the second gas knife) may be the same as theseparation between the lower surface 151 of the fluid handling structure12 adjacent to the one or more openings 71 in the third line and theupper surface of the substrate W and/or substrate table WT. Such anarrangement may therefore allow the separation between the lower surface151 of the fluid handling structure 12 adjacent to the one or moreopenings 71 in the third line and the upper surface of the substrate Wand/or substrate table WT to be reduced, for example minimized. This mayassist in ensuring that the extraction is as effective as possible.However, this need not be the case.

FIG. 14 depicts a fluid handling structure 12 according to an embodimentof the invention. As shown, the fluid handling structure 12 is similarto the fluid handling structure 12 depicted in FIG. 12. The fluidhandling structure of the present embodiment does not include a recess80. However, there is a similar difference between the fluid handlingstructure of this embodiment and the embodiment shown in FIG. 12 to thedifference between the fluid handling structures depicted in FIGS. 13and 10.

The different portions 251 a,251 b,251 c of the lower surface 251 of thefluid handling structure 12 may be arranged such that at least oneportion has a different separation from the upper surface of thesubstrate W and/or the substrate table WT, in use. The separation D2between the lower surface 251 of the fluid handling structure 12adjacent the one or more openings 50 and the upper surface of the facingsurface may be greater than the separation D3 between the lower surface251 of the fluid handling structure 12 adjacent to the aperture 72 andthe upper surface of the facing surface. Each variation describedherein, for example in relation to the embodiments depicted in FIGS. 12and 13 apply to the embodiment depicted in FIG. 14.

In the embodiment depicted in FIG. 14, the lower surface 251 of thefluid handling structure 12 may be arranged such that the difference inseparation between the upper surface of the substrate W and/or substratetable WT and the lower surface 251 changes in the area between theaperture 61 and the one or more openings 71. The separation between thelower surface 251 and the facing surface may vary between the second andthird lines. The separation may change, e.g. decrease, from the secondline to the third line. However, in general the change in separation maybe provided in any or all of the areas between the one or more openings51 and the aperture 72. The separation between the lower surface 251 andthe facing surface may change, e.g. decrease, between the first andfourth lines.

It should be appreciated that, as described above, the lower surface 251of the fluid handling structure 12 may be arranged such that there areno sharp corners at which liquid may be accumulated. The lower surfacemay be substantially continuous between the first and second lines, thesecond and third lines, the third and fourth lines and any combinationof the surfaces between adjacent lines. The lower surface 251 of thefluid handling structure may be arranged such that the minimum radius ofcurvature at any point on the surface is at least 0.1 mm, desirablygreater than 0.2 mm.

Although reference has been made to the use of one or more openings50,302,71 which operate as two phase extractors, in an embodiment basedon any of the variations described herein, the one or more openings ineither the first or fourth lines or the extra extraction 300 may bereplaced by a porous member or microsieve, like that described in U.S.Patent Application Publication No. US 2006-0038968, which is herebyincorporated by reference in its entirety. Each porous member mayoperate to extract liquid in single phase, or dual phase, fluid flow. Inan embodiment, the gas flow may be directed radially inwardly butinstead of if being extracted through the porous member, the gas flowmay be extracted by a gas extraction opening located between the gassupply aperture and the porous member. In such an embodiment the gasflow helps to reduce the residue liquid left on the facing surface bythe gas knife device. An embodiment of the invention may therefore beimplemented in such an arrangement, achieving similar benefits asachieved by the embodiments described above. As will be appreciated, anyof the above described features can be used with any other feature andit is not only those combinations explicitly described which are coveredin this application.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), thin-film magneticheads, etc. The skilled artisan will appreciate that, in the context ofsuch alternative applications, any use of the terms “wafer” or “die”herein may be considered as synonymous with the more general terms“substrate” or “target portion”, respectively. The substrate referred toherein may be processed, before or after exposure, in for example atrack (a tool that typically applies a layer of resist to a substrateand develops the exposed resist), a metrology tool and/or an inspectiontool. Where applicable, the disclosure herein may be applied to such andother substrate processing tools. Further, the substrate may beprocessed more than once, for example in order to create a multi-layerIC, so that the term substrate used herein may also refer to a substratethat already contains multiple processed layers.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength of or about 365, 248, 193, 157 or 126 nm). The term“lens”, where the context allows, may refer to any one or combination ofvarious types of optical components, including refractive and reflectiveoptical components.

Embodiments of the invention are hereinafter described by means of thefollowing clauses:

Clause 1 A fluid handling structure for a lithographic apparatus, thefluid handling structure successively having, at a boundary from a spaceconfigured to contain immersion fluid to a region external to the fluidhandling structure: an elongate opening or a plurality of openingsarranged in a first line that, in use, is directed towards a substrateand/or a substrate table configured to support the substrate; a gasknife device having an elongate aperture in a second line; and anelongate opening or a plurality of openings adjacent the gas knifedevice.

Clause 2 The fluid handling structure according to Clause 1, wherein thefirst and second lines surround the space configured to contain theimmersion fluid; the elongate opening or plurality of openings adjacentthe gas knife device are provided along the length of the gas knifedevice; and respective separations between the first line, second lineand the elongate opening or plurality of openings adjacent the gas knifedevice are substantially the same at all locations around the spaceconfigured to contain the immersion fluid.

Clause 3 The fluid handling structure according to Clause 1 or Clause 2,wherein a separation of the nearest edges of the elongate opening orplurality of openings adjacent the gas knife device and of the elongateaperture of the gas knife device is selected from the range of from 0.25mm to 0.75 mm, desirably 0.5 mm.

Clause 4 The fluid handling structure according to any of Clauses 1 to3, wherein the opening adjacent to the gas knife device is an elongateopening.

Clause 5 The fluid handling structure according to Clause 4, wherein thewidth of the opening adjacent the gas knife device is selected from therange of from 30 μm to 200 μm, or from 100 μm to 150 μm.

Clause 6 The fluid handling structure according to Clause 4 or Clause 5,wherein the edge of the opening adjacent the gas knife device that isclosest to the gas knife device is provided at an oblique angle relativeto the surface of the fluid handling structure that is between the firstand second lines and beyond the opening adjacent the gas knife devicesuch that the width of the opening adjacent the gas knife decreases withdistance from the surface.

Clause 7 The fluid handling structure according to Clause 6, wherein theangle of the edge of the opening adjacent the gas knife device relativeto the surface of the fluid handling structure is selected from therange of from 10° to 60°, or from 10° to 45°, or is desirably 20°.

Clause 8 The fluid handling structure according to any of Clauses 1 to7, wherein the opening adjacent the gas knife device is covered by aporous material.

Clause 9 The fluid handling structure according to any of Clauses 1 to8, wherein the elongate opening or plurality of openings in the firstline and the elongate opening or plurality of openings adjacent the gasknife device are inlets for the passage of a gas and/or liquid into thefluid handling structure.

Clause 10 The fluid handling structure according to any of Clauses 1 to9, wherein the elongate opening or plurality of openings in the firstline are connected, in use, to an under pressure source and the elongateopening or plurality of openings adjacent the gas knife device areconnected, in use, to an under pressure source.

Clause 11 The fluid handling structure according to Clause 10, furthercomprising a controller connected or connectable to the under pressuresource connected to the elongate opening or plurality of openings in thefirst line and/or to the under pressure source connected to the elongateopening or plurality of openings adjacent the gas knife, the controllerconfigured to control the at least one under pressure source such thatthe gas flow rate through the elongate opening or plurality of openingsin the first line and/or the elongate opening or plurality of openingsadjacent the gas knife device is such that, in use, the flow of gas fromthe gas knife device having an elongate aperture in the second line issubstantially perpendicular to the surface of the fluid handlingstructure between the first and second lines.

Clause 12 The fluid handling structure according to any of Clauses 1 to11, wherein, beyond the elongate opening or plurality of openingsadjacent the gas knife device having an elongate aperture in the secondline, the fluid handling structure further successively has at theboundary: an elongate opening or a plurality of openings in a thirdline; and a second gas knife device having an elongate aperture in afourth line.

Clause 13 The fluid handling structure according to Clause 12, whereinthe first to fourth lines successively surround the space configured tocontain the immersion fluid; and separation between the respective linesare substantially the same at all locations around the space configuredto contain the immersion fluid.

Clause 14 The fluid handling structure according to Clause 12 or Clause13, wherein the elongate opening or plurality of openings in the thirdline are inlets for the passage of a gas and/or liquid into the fluidhandling structure.

Clause 15 The fluid handling structure according to any one of Clauses12 to 14, wherein the elongate opening or plurality of openings in thethird line is connected, in use, to an under pressure source, and thefluid handling structure further comprises a controller connected orconnectable to the under pressure source, the controller configured tocontrol the under pressure source such that the gas flow rate throughthe elongate opening or plurality of openings in the third line isgreater than or equal to the gas flow rate out of the aperture in thefourth line to form the gas knife.

Clause 16 The fluid handling structure according to any one of Clauses12 to 15, wherein the apertures in the second and fourth lines areconnected, in use, to a gas supply, and the fluid handling structurefurther comprises a controller connected or connectable to the gassupply, the controller configured to control the gas supply such thatthe gas flow rate out of the aperture in the fourth line to form the gasknife is greater than the gas flow out of the aperture in the secondline to form the gas knife.

Clause 17 A fluid handling structure according to any one of Clauses 12to 16, further comprising a lower surface that, in use, is generallyparallel to an upper surface of a substrate and/or a substrate tableconfigured to support the substrate, and the openings and apertures inthe first to fourth lines are formed in the lower surface.

Clause 18 A fluid handling structure according to Clause 17, wherein inuse, the separations of the area of the lower surface around theopenings and apertures in the first to fourth lines from the uppersurface of the substrate and/or substrate table are substantially thesame.

Clause 19 A fluid handling structure according to Clause 17, wherein inuse, the separation of the area of the lower surface around the elongateopening or plurality of openings in the first line from the uppersurface of the substrate and/or substrate table is greater than theseparation of the area of the lower surface around the aperture in thefourth line from the upper surface of the substrate and/or substratetable.

Clause 20 A fluid handling structure according to any one of Clauses 17to 19, wherein the fluid handling structure comprises a recess in thelower surface, arranged in a fifth line between the second and thirdlines.

Clause 21 A fluid handling structure according to Clause 20, wherein therecess comprises at least one opening that is connected by a gas conduitto the region external to the fluid handling structure.

Clause 22 A fluid handling structure for a lithographic apparatus, thefluid handling structure successively having, at a boundary of a spaceto which in use immersion liquid is confined to a region external to thefluid handling structure: an elongate opening or a plurality of openingsto extract fluid and arranged in a first line that, in use, is directedtowards a facing surface of, for example, a substrate and/or a substratetable configured to support the substrate; an elongate aperture for agas knife, in a second line; an elongate opening or a plurality ofopenings to extract liquid and formed adjacent the elongate aperture forthe gas knife.

Clause 23 The fluid handling structure of Clause 22, wherein theelongate opening or the plurality of openings in the first line is topin a meniscus of the immersion liquid in the space.

Clause 24 A lithographic apparatus, comprising a fluid handlingstructure according to any one of the preceding Clauses.

Clause 25 A device manufacturing method, comprising: providing animmersion liquid to a space between a final element of a projectionsystem and a substrate and/or a substrate table configured to supportthe substrate; retrieving immersion liquid from between the finalelement of the projection system and the substrate and/or substratetable through an elongate opening or a plurality of openings arranged ina first line; forcing immersion liquid towards the elongate opening orplurality of openings in the first line by supplying gas through anaperture in a second line forming a gas knife; extracting gas andremaining immersion liquid through an elongate opening or a plurality ofopenings adjacent the gas knife and on the opposite side of the gasknife to the elongate opening or plurality of openings in the firstline.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. For example, the embodiments of the invention maytake the form of a computer program containing one or more sequences ofmachine-readable instructions describing a method as disclosed above, ora data storage medium (e.g. semiconductor memory, magnetic or opticaldisk) having such a computer program stored therein. Further, themachine readable instruction may be embodied in two or more computerprograms. The two or more computer programs may be stored on one or moredifferent memories and/or data storage media.

The controllers described herein may each or in combination be operablewhen the one or more computer programs are read by one or more computerprocessors located within at least one component of the lithographicapparatus. The controllers may each or in combination have any suitableconfiguration for receiving, processing, and sending signals. One ormore processors are configured to communicate with the at least one ofthe controllers. For example, each controller may include one or moreprocessors for executing the computer programs that includemachine-readable instructions for the methods described above. Thecontrollers may include data storage medium for storing such computerprograms, and/or hardware to receive such medium. So the controller(s)may operate according the machine readable instructions of one or morecomputer programs.

One or more embodiments of the invention may be applied to any immersionlithography apparatus, in particular, but not exclusively, those typesmentioned above and whether the immersion liquid is provided in the formof a bath, only on a localized surface area of the substrate, or isunconfined. In an unconfined arrangement, the immersion liquid may flowover the surface of the substrate and/or substrate table so thatsubstantially the entire uncovered surface of the substrate table and/orsubstrate is wetted. In such an unconfined immersion system, the liquidsupply system may not confine the immersion fluid or it may provide aproportion of immersion liquid confinement, but not substantiallycomplete confinement of the immersion liquid.

A liquid supply system as contemplated herein should be broadlyconstrued. In certain embodiments, it may be a mechanism or combinationof structures that provides a liquid to a space between the projectionsystem and the substrate and/or substrate table. It may comprise acombination of one or more structures, one or more fluid openingsincluding one or more liquid openings, one or more gas openings or oneor more openings for two phase flow. The openings may each be an inletinto the immersion space (or an outlet from a fluid handling structure)or an outlet out of the immersion space (or an inlet into the fluidhandling structure). In an embodiment, a surface of the space may be aportion of the substrate and/or substrate table, or a surface of thespace may completely cover a surface of the substrate and/or substratetable, or the space may envelop the substrate and/or substrate table.The liquid supply system may optionally further include one or moreelements to control the position, quantity, quality, shape, flow rate orany other features of the liquid. In an embodiment, the immersion liquidmay be water.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the invention as described without departing from thescope of the claims set out below.

The invention claimed is:
 1. A fluid handling structure for alithographic apparatus, the fluid handling structure having, at a lowerside and outward from a region configured to contain immersion fluid: afirst elongate opening or plurality of openings arranged in a first lineor curve that, in a use, is directed towards a substrate in thelithographic apparatus and/or a towards a substrate table of thelithographic apparatus, the substrate table configured to support thesubstrate; a first gas knife device having an elongate aperture orplurality of openings in a second line or curve; a second elongateopening or plurality of openings adjacent the first gas knife device,the second elongate opening or plurality of openings adjacent the firstgas knife device arranged in a multi-sided shape around the region;outward, relative to the region, of the second elongate opening orplurality of openings adjacent the first gas knife device, a thirdelongate opening or plurality of openings in a third line or curve; anda second gas knife device having an elongate aperture or plurality ofopenings in a fourth line or curve, wherein each of the first to fourthlines or curves surround the region and a separation between therespective lines or curves are substantially the same at all locationsaround the region.
 2. The fluid handling structure according to claim 1,wherein a separation of the nearest edges of the second elongate openingor plurality of openings adjacent the first gas knife device and of theelongate aperture or plurality of openings of the first gas knife deviceis selected from the range of from 0.25 mm to 0.75 mm.
 3. The fluidhandling structure according to claim 1, wherein the second elongateopening or plurality of openings adjacent to the first gas knife devicecomprises an elongate opening.
 4. The fluid handling structure accordingto claim 3, wherein the width of the second opening adjacent the firstgas knife device is selected from the range of from 30 μm to 200 μm. 5.The fluid handling structure according to claim 1, wherein the secondelongate opening or plurality of openings adjacent the first gas knifedevice is covered by a porous material.
 6. The fluid handling structureaccording to claim 1, wherein the second elongate opening or pluralityof openings adjacent the first gas knife device is for the passage of agas and/or liquid into the fluid handling structure.
 7. The fluidhandling structure according to claim 1, wherein the third elongateopening or plurality of openings in the third line or curve are inletsfor the passage of a gas and/or liquid into the fluid handlingstructure.
 8. The fluid handling structure according to claim 1, whereinthe third elongate opening or plurality of openings in the third line orcurve is connected, in use, to an under pressure source, and the fluidhandling structure further comprises a controller connected orconnectable to the under pressure source, the controller configured tocontrol the under pressure source such that the gas flow rate throughthe third elongate opening or plurality of openings in the third line orcurve is greater than or equal to the gas flow rate out of the elongateaperture or plurality of openings in the fourth line or curve to formthe gas knife.
 9. The fluid handling structure according to claim 1,wherein the apertures and openings in the second and fourth lines orcurves are connected, in use, to a gas supply, and the fluid handlingstructure further comprises a controller connected or connectable to thegas supply, the controller configured to control the gas supply suchthat the gas flow rate out of the elongate aperture or plurality ofopenings in the fourth line or curve to form the second gas knife isgreater than the gas flow out of the elongate aperture or plurality ofopenings in the second line or curve to form the first gas knife. 10.The fluid handling structure according to claim 1, further comprising alower surface that, in use, is generally parallel to an upper surface ofa substrate and/or a substrate table configured to support thesubstrate, and the openings and apertures in the first to fourth linesor curves are formed in the lower surface.
 11. The fluid handlingstructure according to claim 10, wherein in use, the separations of thearea of the lower surface around the openings and apertures in the firstand second lines or curves from the upper surface of the substrateand/or substrate table are greater than the separations of the area ofthe lower surface around the openings and apertures in the third andfourth lines or curves from the upper surface of the substrate and/orsubstrate table.
 12. A fluid handling structure for a lithographicapparatus, the fluid handling structure having, at a lower side andoutward from a region configured to contain immersion fluid: a firstelongate opening or plurality of openings arranged in a first line orcurve that, in a use, is directed towards a substrate in thelithographic apparatus and/or a towards a substrate table of thelithographic apparatus, the substrate table configured to support thesubstrate; a first gas device having an elongate aperture or pluralityof openings in a second line or curve, the first gas device configuredto supply gas toward the substrate and/or substrate table; a secondelongate opening or plurality of openings having a porous member andlocated outward, relative to the region, of the first line or curve, thesecond elongate opening or plurality of openings having the porousmember arranged in a multi-sided shape around the region; a thirdelongate opening or plurality of openings in a third line or curve andlocated outward, relative to the space, of the second line; and a secondgas device having an elongate aperture or plurality of openings in afourth line or curve and located outward, relative to the space, of thethird line or curve, the second gas device configured to supply gastoward the substrate and/or substrate table.
 13. The fluid handlingstructure according to claim 12, wherein the second elongate opening orplurality of openings having the porous member and the third elongateopening or plurality of openings in the third line or curve are for thepassage of a gas and/or liquid into the fluid handling structure. 14.The fluid handling structure according to claim 12, wherein the thirdelongate opening or plurality of openings in the third line or curve hasa porous member.
 15. The fluid handling structure according to claim 12,wherein, in use, the separations of an area of a lower surface of thefluid handling structure around the openings and apertures in the firstand second lines or curves from an upper surface of the substrate and/orsubstrate table are greater than the separations of an area of the lowersurface around the openings and apertures in the third and fourth linesor curves from the upper surface of the substrate and/or substratetable.
 16. A fluid handling structure for a lithographic apparatus, thefluid handling structure having, at a lower side and outward from aregion configured to contain immersion fluid: an elongate opening orplurality of openings arranged in a first line or curve that, in a use,is directed towards a substrate in the lithographic apparatus and/or atowards a substrate table of the lithographic apparatus, the substratetable configured to support the substrate; a first gas device having anelongate aperture or plurality of openings in a second line or curve,the first gas device configured to supply gas toward the substrateand/or substrate table; a first elongate opening or plurality ofopenings located outward, relative to the region, of the first line orcurve, the first elongate opening or plurality of openings arranged in amulti-sided shape around the region; a second elongate opening orplurality of openings located outward, relative to the region, of thefirst elongate opening or plurality of openings; an elongate opening orplurality of openings in a third line or curve and located outward,relative to the space, of the second elongate opening or plurality ofopenings; and a second gas device having an elongate aperture orplurality of openings in a fourth line or curve, the second gas deviceconfigured to supply gas toward the substrate and/or substrate table.17. The fluid handling structure according to claim 16, wherein thefirst elongate opening or plurality of openings is for the passage of agas and/or liquid into the fluid handling structure.
 18. The fluidhandling structure according to claim 16, wherein the Ran secondelongate opening or plurality of openings are for the passage of gastherethrough.
 19. The fluid handling structure according to claim 16,wherein the first elongate opening or plurality of openings and theelongate opening or plurality of openings in the third line or curve arefor the passage of a gas and/or liquid into the fluid handlingstructure.
 20. The fluid handling structure according to claim 16,further comprising a lower surface that, in use, is generally parallelto an upper surface of a substrate and/or a substrate table configuredto support the substrate, and the openings and apertures in the first tofourth lines or curves are formed in the lower surface.